LMA. The LMA approach is common, and available in many computer programs, such as PhreeqC, Minteq2, Wateq4f3, EQ3/64, Chess/JChess5, The Geochemist’s Workbench6 and others. The program aqion, that relies on the numerical solver of PhreeqC, belongs to the LMA category as well.

GEM. The GEM approach, represented by codes such as Solgasmix7, ChemSage8, FactSage9, Selektor10 or GEMS-PSI11, is less common, but is becoming increasingly popular.

The mathematical treatment of the equilibrium speciation problem yields nonlinear equation systems that can only be solved iteratively (such as root finding with Newton-Raphson method and other techniques). Thus, the application of numerical computer programs is a natural consequence.